1. Field of the Invention
The present invention relates generally to the field of cementing well pipes into a well. More specifically, the present invention relates to methods and apparatuses for cementing a string of well pipe in a wellbore with a self-filling cementing collar.
2. Setting of the Invention
U.S. Pat. No. 5,641,021, assigned to the Assignee of the present invention, describes a well casing fill apparatus and methods for filling a casing string with wellbore fluid while running a string into a wellbore and cementing the casing into the wellbore. This patented prior art well casing fill apparatus is comprised of a tubular housing having a wellbore fluid fill port extending through a housing wall and a closing sleeve slidably disposed in the tubular housing movable axially between an upper position in which the fluid fill port is open and a lower position in which the fill port is closed by the sliding sleeve. A landing seat on the closing sleeve receives a cementing plug to slide the closing sleeve to the closed position. A one-way check valve in a casing shoe at the foot of the fill apparatus prevents fluid from entering the casing but opens to allow cement in the casing to exit from the casing shoe bottom.
The patented prior art device is capable of permitting the casing string to self-fill quickly, while minimizing hydraulic forces generated on subterranean strata as a result of running the casing string into a fluid filled wellbore. If, however, it becomes necessary to circulate through the end of the casing string shoe, as may be required for example to wash the casing string past an obstruction, the closing sleeve must be shifted down to close the fill ports so that the circulating fluid will exit from the bottom of the casing. Once the closing sleeve has been shifted to the closed position, the automatic fill function of the fill apparatus becomes permanently disabled. Subsequent lowering of the casing into the wellbore requires that the casing string be lowered very slowly to prevent the creation of hydraulic ram forces that can break down formations below the casing. The disabling of the self-fill apparatus may also require that fill fluid be added from the well surface as the casing string is lowered, which further slows and complicates the casing running process.
The circulating cementing collar of the present invention provides self-filling, one-way flow of well fluids into a casing string from a fluid filled wellbore while the casing string is being lowered into the wellbore and automatically permits forward circulation of fluid through the end of the casing when desired without disabling the self-fill function. The cementing collar of the present invention may be cycled between its self-filling function and its forward circulation function as often as required during placement of the casing in the wellbore.
In one form of the invention, an axially movable sleeve carried within the cementing collar is equipped with one-way flow passages that permit the casing string to self-fill with well fluids that enter the casing string from fill passages extending through the wall of the collar. The one-way flow passages are provided with valving that prevents a reverse flow of fluids from the casing through the fill passages. In operation, the one-way flow passages remain open as the casing is being lowered into the fluid filled wellbore, thereby permitting the well fluid to automatically fill the casing while minimizing the imposition of hydraulic ramming forces against the subsurface formation. If forward circulation through the casing becomes necessary, well fluid may be pumped from the surface through the casing, closing the one-way valving of the fill passages and forcing the fluid to exit the end of the casing. Fluid exiting the lowermost end of the casing string is effectively applied directly against any bridging material or other obstruction that initiated the requirement for forward circulation.
The self-filling action is permanently disabled when the cement slurry is pumped into the casing string to prevent back-flow of the cement into the casing through the fill passages.
From the foregoing, it will be appreciated that a primary object of the present invention is to provide a self-filling cementing device that permits conversion from a self-filling function in which well fluids are automatically admitted into the casing string to a forward circulation function in which well fluids are circulated from the bottom of the casing string while maintaining the ability to automatically revert to the self-filling function following termination of the forward circulation function.
Another object the present invention is to provide a low-cost cementing collar that can be fabricated from inexpensive, simply manufactured components and that permits self-filling of a well casing while maintaining the capability at anytime during the placement of the casing in the wellbore to initiate forward circulation through the cementing collar as required to wash past an obstruction in the wellbore and thereafter revert to a self-filling function as the casing is lowered further into the wellbore.
Yet another object of the present invention is to provide a cementing device that permits conversion between self-filling of the casing string and forward circulation of fluids through the string as often as required while lowering the casing string into the wellbore and that further permits the self-filling function to be remotely terminated when the casing has been positioned at the desired location within the wellbore to prevent flow back of fluid through the self-fill passages.
An important object of the present invention is to provide one-way flow valving in a subsurface circulating cement collar with a design that employs low cost, easy to fabricate components and in which the components effect one-way flow control without the requirement for precise dimensional tolerances or special materials.
The foregoing features, advantages and objects of the present invention will be more fully understood and better appreciated by reference to the following drawings, specification and claims.